Typically, as a well is drilled, the casing becomes smaller as the well is drilled deeper. The reduction in size of the casing restrains the size of tubing that can be run into the well for ultimate production. Additionally, if existing casing becomes damaged or needs repair, it is desirable to insert a patch through that casing and be able to expand it downhole to make a casing repair, or in other applications to isolate an unconsolidated portion of a formation that is being drilled through by running a piece of casing in the drilled wellbore and expanding it against a soft formation, such as shale.
Various techniques of accomplishing these objectives have been attempted in the past. In one technique developed by Shell Oil Company and described in U.S. Pat. No. 5,348,095, a hydraulically actuated expanding tool is inserted in the retracted position through the tubular casing to be expanded. Hydraulic pressure is applied to initially expand the tubular member at its lower end against a surrounding wellbore. Subsequently, the hydraulic pressure is removed, the expanding tool is lifted, and the process is repeated until the entire length of the casing segment to be expanded has been fully expanded from bottom to top. One of the problems with this technique is that it is uncertain as to the exact position of the expanding tool every time it is moved from the surface, which is thousands of feet above where it is deployed. As a result, there's no assurance of uniform expansion throughout the length of the casing to be expanded using this technique. Plus, the repeated steps of application and withdrawal of hydraulic pressure, coupled with movements in the interim, are time-consuming and do not yield with any certainty a casing segment expanded along its entire length to a predetermined minimum inside diameter. U.S. Pat. No. 5,366,012 shows a perforated or slotted liner segment that is initially rigidly attached to the well casing and expanded by a tapered expansion mandrel. This system is awkward in that the slotted liner with the mandrel is installed with the original casing, which requires the casing to be assembled over the mandrel.
Other techniques developed in Russia and described in U.S. Pat. Nos. 4,976,322; 5,083,608; and 5,119,661 use a casing segment which is specially formed, generally having some sort of fluted cross-section. The casing segment to be expanded which has the fluted shape is subjected to hydraulic pressure such that the flutes flex and the cross-sectional shape changes into a circular cross-section at the desired expanded radius. To finish the process, a mechanical roller assembly is inserted into the hydraulically expanded fluted section. This mechanical tool is run from top to bottom or bottom to top in the just recently expanded casing segment to ensure that the inside dimension is consistent throughout the length. This process, however, has various limitations. First, it requires the use of a pre-shaped segment which has flutes. The construction of such a tubular shape necessarily implies thin walls and low collapse resistance. Additionally, it is difficult to create such shapes in a unitary structure of any significant length. Thus, if the casing segment to be expanded is to be in the order of hundreds or even thousands of feet long, numerous butt joints must be made in the fluted tubing to produce the significant lengths required. Accordingly, techniques that have used fluted tubing, such as that used by Homco, now owned by Weatherford Enterra Inc., have generally been short segments of around the length of a joint to be patched plus 12-16 ft. The technique used by Hornco is to use tubing that is fluted. A hydraulic piston with a rod extends through the entire segment to be expanded and provides an upper travel stop for the segment. Actuation of the piston drives an expander into the lower end of the specially shaped fluted segment. The expander may be driven through the segment or mechanically yanked up thereafter. The shortcoming of this technique is the limited lengths of the casing to be expanded. By use of the specially made fluted cross-section, long segments must be created with butt joints. These butt joints are hard to produce when using such special shapes and are very labor-intensive. Additionally, the self-contained Homco running tool, which presents an upper travel stop as an integral part of the running tool at the end of a long piston rod, additionally limits the practical length of the casing segment to be expanded.
What is needed is an apparatus and method which will allow use of standard pipe which can be run in the wellbore through larger casing or tubing and simply expanded in any needed increment of length. It is thus the objective of the present invention to provide an apparatus and technique for reliably inserting the casing segment to be expanded and expanding it to a given inside dimension, while at the same time accounting for the tendency of its overall length to shrink upon expansion. Those and other objectives will become apparent to those of skill in the art from a review of the specification below.